Generally, it is important for a semiconductor element such as a semiconductor laser element and a high-frequency element used in optical communication or the like to efficiently release heat generated from the element, in order to prevent malfunction or the like. Recently, technological development of semiconductor elements has promoted high power, high speed and high integration of the elements, and a demand for heat dissipation has become increasingly more challenging. Thus, in general, a high thermal conductivity has also been required for heat dissipation components such as heat sinks, and copper (Cu) having a high thermal conductivity of 390 W/mK has been used.
On the other hand, the size of individual semiconductor element has been increased with an increase in output power, and a problem of a thermal expansion mismatch between the semiconductor element and the heat sink used for heat dissipation have become apparent. To solve the problem, there is a need for development of a heat sink material that achieves both a property of high thermal conductivity and the matching with a coefficient of thermal expansion of the semiconductor element. As such a material, a prior art proposes a composite of a metal and a ceramic, for example, a composite of aluminum (Al) and silicon carbide (SiC) (Patent Document 1).
However, the Al—SiC composite only has a thermal conductivity of 300 W/mK or less even if the conditions are optimized. Therefore, there is a need for development of a heat sink material having further higher thermal conductivity than that of copper. As such a material, a prior art proposes a metal-diamond composite having a high thermal conductivity and a coefficient of thermal expansion close to that of the semiconductor element, by a combination of the high thermal conductivity of diamond and the large coefficient of thermal expansion of a metal (Patent Document 2).
Further, patent document 3 discloses that the forming of p-type SiC layers on the surface of diamond particles suppresses generation of a metal carbide having a low coefficient of thermal expansion formed during production of a composite and improves wettability to a molten metal, thereby improving a thermal conductivity of a diamond composite material obtained.
Furthermore, diamond is a very hard material. Therefore, the metal-diamond composite obtained by compounding diamond with the metal is also very hard and is difficult to process. For this reason, the metal-diamond composite can hardly be processed with ordinary diamond tools, and has a problem of how to process it with a lower cost in order to use the metal-diamond composite for heat sinks that are small and has various shapes. To solve the problem, a method for processing the metal-ceramic composite has been studied, such as laser processing and water jet processing. Since the metal-ceramic composite can be energized, electric discharge machining has also been studied.